Valves are lanceolate-clavate, widest at the center. The headpole and footpole are narrowly rounded. The axial area is large and lanceolate. The raphe is filiform, with weakly expanded proximal ends that are bent slightly to one side. Striae are uniseriate and very short. The striae are parallel at the valve center and radiate near the apices.
Note that G. camburnii and G. patrickii are heterotypic, or subjective, synonyms of this taxon.
Gomphonema louisiananum was described from material collected at a reservoir in northwestern Louisiana and subsequently reported (as G. patricki) from a lake in the Sierra Nevada Mountains of California (Kociolek et al. 1995). This taxon has also been reported from a stream in South Carolina (Camburn et al. 1978), from low-alkalinity lakes in Minnesota and New York (Camburn and Charles 2000), and from a river in Brazil (Metzeltin and Lange-Bertalot 1998). It was recently found in samples collected from a subalpine lake in the Eagle Cap Wilderness of northeastern Oregon and a lake near sea level on the Haida Gwaii Archipelago of British Columbia (photos below). Although environmental data are not available for these sites, they are primarily sites that have little human influence.
Valve lanceolate, evenly narrowed toward the apex and basis, apex slightly broader. Axial and central area forming a broad lanceolate area. Striae uniformly shortened, slightly radiate throughout most of the valve to almost parallel at the apex. Striae, 12-13 in 10 µm at the centre of the valve to 15 in 10 µm near the apices. Length, 13-30 µm. Breadth, 3-5 µm.
Prior to this date, length was documented as 17.2-29.1 µm, width as 4.0-5.4 µm. These values were revised to reflect the length and width of a recently found robust population of this taxon. New images from this Eleanor Creek population have replaced those from Oregon and British Columbia. - I. Bishop
Bahls, L., Bishop, I. (2013). Gomphonema louisiananum. In Diatoms of North America. Retrieved October 30, 2024, from https://diatoms.org/species/gomphonema_louisiananum
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Gomphonema louisiananum from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:
ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.